EP 1 121 544 B1 describes a piston for a piston-cylinder arrangement, particularly a shock absorber piston, which has a piston body with a circumferential surface and a sealing collar. The sealing collar has an outer circumferential surface, an inner circumferential surface, a first peripheral surface and a first sealing lip and extends around the circumferential surface of the piston body and covers at least part of the circumferential surface in the axial direction. The first peripheral surface connects the two circumferential surfaces to each other at a first end of the sealing collar. The sealing lip is delimited by the first peripheral surface and the outer circumferential surface and projects out radially from the outer circumferential surface.
EP 1 121 544 B1 moreover describes a method for producing such piston where a sealing blank and a piston body are provided, the sealing blank is then pushed over the piston body, and the sealing blank is pressed against the piston body. With this known piston, the sealing collar consists of a thermoplastic material, preferably of PTFE (polytetrafluoroethylene), and according to this known method is molded by thermoforming onto the circumferential surface of the piston body from a circular washer which represents the sealing blank. For this purpose, the circular washer, or the sealing blank, is fitted onto one end of the piston body and the piston body that is prepared in this way is pressed into a heated forming and calibration cylinder, wherein the circular washer is placed as a band around the circumferential surface of the piston body and is subsequently pressed against the circumferential surface of the piston body under the influence of heat. In this instance, the piston body is provided with at least one peripheral web which is to ensure a perfect and reliable connection between the sealing collar and the piston body. The piston with its pressed-on sealing collar is then finally guided through a cooling tube. The “back memory” phenomenon of the plastic material of the sealing collar has the effect that after the forming, the one edge of the sealing collar, which is formed by the inside edge of the circular washer contracts inward, and the other, opposite edge of the sealing collar, which is formed by the outer edge of the circular washer, repositions itself to the outside and on this occasion projects beyond the remaining circumferential surface of the sealing collar, similar to a sealing lip.
The sealing lip of this known piston is therefore generated in this known process in that the sealing collar remembers its original form of the circular washer. This known piston and this known method have the disadvantage that the sealing lip is highly corrugated, because of the internal stresses that are formed as a result of manufacturing during the forming of the circular washer into the sealing collar, which can impair the sealing function.
DE 195 13 727 B4 also describes a piston as well as a method for producing such piston. This known piston also has a support element and a guide ring that at least partially encloses the support element on its outside, where said guide ring is of polymeric material, preferably of PTFE. The support element has at least one circumferential radial groove that is open in the direction of the guide ring, where said groove engages radially into the assembly-related projection of the guide ring. The guide ring on each of its two sides has an assembly-related, one-piece molded sealing lip which extends in a radial direction. The sealing lips protrude the contact surface element of the support in an axial direction. In this known method, the blank of the guide ring is pushed over the outside of the support element and is subsequently molded exclusively radially evenly full-circumferentially until the condition of the guide ring material is no longer flowable. Because the material of the guide ring starts to flow in this context, the grooves of the support element are filled completely by the material of the guide ring. While the material of the guide ring gradually flows into the grooves of the carrier element and fills them, portions of this material flow as a result of the radial molding in an axial direction along the circumferential surface of the carrier element and form the sealing lips. The sealing lips are thus formed as a result of the guide ring material which is diverted in a radial direction during the radial molding.
This known piston and this known method have the disadvantage that due to the manufacturing, the sealing lips have a relatively poor fabrication precision, since the material of the guide ring can freely flow in the axial direction during the radial compression.